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Chapter 4 (English)

1. Mass Storage Structure

Mass Storage Structure – Overview in OS

Mass storage refers to non-volatile storage devices used by an operating system to store data permanently. This includes hard disk drives (HDDs), solid-state drives (SSDs), optical disks, and other large-capacity storage media. The OS manages these devices to provide efficient, reliable access to data. The mass storage structure in OS can be understood in layers:

 

1. Physical Storage Layer

  • Definition: The actual hardware where data is stored.
  • Examples: HDD platters, SSD flash cells, magnetic tapes.
  • Characteristics:
    • Data is organized in blocks or sectors.
    • Access times vary depending on device type.
    • Storage is divided into tracks and sectors in HDDs.

 

2. Logical Storage Layer

  • Definition: How the OS abstracts physical storage into logical units for easier management.
  • Components:
    • Blocks or Sectors: Smallest unit of data transfer (usually 512 bytes or 4 KB).
    • Logical Block Addressing (LBA): The OS refers to storage locations using logical addresses instead of physical locations.
    • Partitions: Dividing the storage device into independent logical areas, each possibly containing a file system.

 

3. File System Layer

  • Definition: A structured way to store, retrieve, and organize files on mass storage.
  • Key Functions:
    • Mapping file names to data blocks.
    • Managing free space and allocation.
    • Maintaining metadata like file size, creation date, permissions.
  • Common File Systems:
    • Windows: NTFS, FAT32
    • Linux: ext4, XFS
    • macOS: APFS

 

4. Access Methods

  • Definition: How the OS allows programs to read/write data.
  • Types:
    • Sequential Access: Data is read/written in order (e.g., tape storage).
    • Direct Access (Random Access): Data can be read/written at any location (e.g., HDD, SSD).

 

5. Storage Management by OS

  • Disk Scheduling: Optimizes read/write operations for speed (e.g., FCFS, SSTF, SCAN algorithms).
  • Buffering: Temporary storage of data to balance speed differences between CPU and disk.
  • Caching: Keeps frequently accessed data in faster memory (RAM).
  • RAID Management: Some OSs handle Redundant Array of Independent Disks for fault tolerance and performance.